Contents

Hardware

The vendor specifically announces the high IP rating, and the advanced safety features.
The labelling suggests that "ASYC" stands for "Advanced Safety Concept".
Some models "lock" the probes, such that special action needs to be taken before they can get unplugged.
The battery and fuse compartment only can get accessed after the probes were removed.

The tilt stand at the back of the device can get removed, and then be used as a tool to open the front cover.
The locations for the tool during this activity are marked.
Removing the front cover allows access to the battery and the fuses.
The tool can be used to further open the device and remove the back cover as well, to access the PCB inside the meter.
But that activity is not suggested, and is not needed for regular use.

The location of the IR LEDs is rather unusual -- right underneath the range selector, within the battery compartment.
This is especially annoying as the meter has a high IP rating, which results in extra covers for improved isolation from environmental influences.
A special kit is sold for serial communication, which includes an alternative cover that replaces the originally shipped cover around the range selector.

(No further hardware details here, neither teardown images -- see the EEVblog link in the resources section.
Images there show a DMM chip labelled "ITT" and "METRIX DMM5", and a flyer for the serial communication kit.
User "free_electron" provides background on the ITT corporation.)

Photos

front view, with holster

back view, button and power-on instructions

display, bargraph, ASYC(R) II label, IP67 rating

battery compartment, IR LED location

battery compartment, model name, rubber cover, tilt stand

Protocol

Dumb mode (PRINT button)

When the user presses the PRINT button, the meter periodically sends measurement data via IR.
Holding the PRINT button allows adjustment of the interval (seconds resolution, up to 10 hours).
The PRINT button needs to get pressed again each time the function selection is changed.

Data is communicated via UART frames in 8n1 format at 2400bps.
All communicated bytes are in the ASCII range.
Each packet consists of 16 bytes which includes the CR terminator.
The packet contains a (signed) number value, then scale factor and unit for the measurement, and optional flags.
The absence of separators between the packet's fields makes case _sensitive_ parsing essential,
case insensitive operation would become ambiguous and would even break successful operation of the driver.

The sigrok driver currently only implements support for this PRINT mode.

Smart mode ("RS 232 mode")

When the PK button is pressed at power-on, "RS 232 mode" gets enabled.
All operation still is controlled by the meter's range selector and buttons, but UART communication via IR becomes bidirectional.
The peer can query the current mode and state (and needs to reflect on that in its subsequent communication, the available documentation explicitly warns about sending commands that don't match the meter's capabilities or mode!).
The peer can request the previous or a next measurement, which might result in higher update rates compared to the PRINT mode.

Requests and responses in this mode are variable width (model dependent!), and "mostly ASCII" with occasional use of control characters.
While packets are of variable length, there are no record separators which would allow for synchronization to the data stream, or recognition of frame borders independently from (assumed) presence of a specific model.
Maybe a sequence of ESC and ENQ/ACK might help when synchronization was lost.
See the ASYC2 related PDF in the resources section for details.